EXCEED THE SPACE PROVIDED. This is an application for the Data Management Center for the Carotid Occlusion Surgery Study (COSS). The COSS research team is made up of the Clinical Coordinating Center (CCC) at Washington University in St. Louis and the Data Management Center at The University of Iowa. Dr. William Powers is the Principal Investigator for COSS and the Director of the Clinical Coordinating Center. He has prepared a sister proposal. The two are intended to be reviewed together. The goal of this study is to test the hypothesis that extra cranial-intra cranial (EC/IC) arterial bypass by surgical anastomosis of the superficial temporal artery to the middle cerebral artery (STA-MCA) when added to best medical therapy can reduce by 40%, despite perioperative stroke and death, subsequent ipsilateral ischemic stroke at two years in patients with recently symptomatic internal carotid artery occlusion and Stage II hemodynamic failure. The Data Management Center will be responsible for designing and implementing the database and web-based distributed data entry system and the central randomization system for COSS. It will be responsible for ensuring the timely and complete capture of data into the database and for ensuring that the data are valid. It will also conduct twice-annual site monitoring visits at each participating clinical site. DMC investigators and staff will work with Drs Powers and Grubb and the study investigators to design the interim and final data analyses and will .perform all statistical analyses and prepare reports from those analyses. The center will also support the activities of the Surgical and Safety Committee and the Endpoint Adjudication Committee. Investigators and staff from the DMC will participate in the twice-monthly conference calls with the CCC and will attend the face-to-face meetings that will occur at alternate sites six times a year.